Milk thistle extract buyer's guide: silymarin grades and specs
The number we always state separately. In our own quotations we list the silymarin assay (HPLC) and the silybin assay (HPLC) on separate lines, because a brand's QA team will ask for both — and because a single blended figure is how label-claim disputes start. A typical lot from our standard grade reads silymarin 80.6% with silybin 31.2%, and both numbers appear on the COA that ships with the goods.
Ask three suppliers for milk thistle extract and you will get three prices and, quite often, three different sets of numbers. Liver support is one of the largest categories in the U.S. supplement market, and milk thistle is the ingredient most of those formulas are built around. This guide is about making the numbers comparable before price enters the conversation.
What milk thistle extract is
Milk thistle extract is a preparation of the seed of Silybum marianum (L.) Gaertn., extracted with food-grade ethyl acetate or ethanol. The active benchmark is silymarin — and the first thing to understand is that silymarin is not a single compound. It is a defined group of flavonolignans: silybin, isosilybin, silychristin and silydianin together.
That distinction drives everything else:
- Silymarin is the family total. It is the figure most specifications and most labels are written around.
- Silybin is the principal component of that family and the figure a quality-focused brand usually insists on separately.
A specification that names only a silymarin percentage — without naming the method and without the silybin figure — is incomplete, and incomplete specifications are where orders go wrong.
The grades that matter
The grade most U.S. liver-support products are formulated around is silymarin 80% by HPLC. It is the standard production grade, and it is the grade most quotations you receive will quote. Two alternatives exist, and each solves a specific formulation problem:
| Grade | Typical use | Notes |
|---|---|---|
| Silymarin 80% (HPLC) | Capsules and tablets | Standard production grade; silybin 30%–98% available |
| Silymarin 70% | Cost-sensitive formulations | Alternative assay; confirm the method named |
| Water-dispersible 20% | Beverages, stick packs | For applications where 80% powder will not disperse |
Our standard grade is a yellow-brown fine powder at 80 mesh (100 mesh on request), extracted with food-grade ethyl acetate or ethanol, with no carrier — a pure extract. Maltodextrin-carried versions can be produced if your process needs them.
Why the assay method decides the number
Here is the part that catches first-time buyers. Silymarin can be measured by UV or by HPLC, and the two methods give different numbers for the same powder. A UV-based figure typically reads higher than an HPLC figure. Neither method is dishonest — but a quotation that says "silymarin 80%" without naming the method is not comparable with one that says "silymarin 80% by HPLC."
We standardise and report silymarin by HPLC, and we report silybin as a separate line on the COA. That is what allows your label claim to be traced to a number if a customer, a retailer or a regulator asks. It costs more per lot to run, and it is the difference between a specification you can defend and one you cannot.
Rule of thumb: if a quotation does not name the assay method next to the percentage, treat the number as unverified until the supplier confirms it in writing.
What a serious COA shows
The COA is where specification discipline becomes visible. A typical lot of our standard grade reads as follows:
- Silymarin (HPLC) 80.6% against a specification of ≥ 80%
- Silybin (HPLC) 31.2%
- Loss on drying 4.1% against a limit of ≤ 5.0%; total ash 1.9%
- Residual ethyl acetate below 300 ppm — within ICH Q3C limits, and the actual figure printed on the COA
- Lead below 1 ppm, arsenic below 0.5 ppm, cadmium below 0.2 ppm
- Total plate count below 1,000 cfu/g; yeast and mould below 100 cfu/g; Salmonella and E. coli negative
Two lines on that list deserve attention. First, residual solvents: many suppliers leave them off the COA entirely. The figure being present — and within ICH Q3C limits — is itself a quality signal. Second, heavy metals: U.S. buyers increasingly ask for Proposition 65-relevant metals, and a COA that reports lead, arsenic and cadmium with actual figures rather than "conforms" saves an email round.
What to ask for before your first order
Before committing to a supplier, ask for five documents. A serious supplier will send all of them without hesitation:
- The specification sheet for the exact grade, with methods named next to every figure.
- A sample COA from a recent production lot — not a generic document, an actual lot.
- The allergen, non-GMO and (if relevant) kosher/halal statements.
- SDS for the extract.
- A pre-shipment sample drawn from the actual production lot, not from a retained sample of an earlier batch.
On quantity: pilot runs of 5 kg or 10 kg are quotable before you commit to a full order, with higher per-kilogram pricing confirmed in the quotation. Standard packing is 25 kg fibre drums with a double polyethylene liner, shelf life 24 months unopened, stored cool, dry and away from direct sunlight. Lead times: in-stock items ready in about 2 days; bulk production 3–5 working days after deposit for standard grades; transit Xi'an → Shenzhen consolidation about 3 days, then roughly 6 days by air to major U.S. and EU airports, or 18–25 days by sea.
Where this leaves you
Milk thistle is a competitive category, but the specification discipline above is not universal among suppliers. If you are comparing quotations right now, the fastest filter is simple: name the method next to every percentage, ask for the silybin figure separately, and check whether residual solvents appear on the COA with a number. Most of the field fails at least one of those three.
Frequently asked questions
What is the difference between silymarin and silybin?
Silymarin is the defined group of flavonolignans from milk thistle seed — silybin, isosilybin, silychristin and silydianin together — and it is the figure most specifications and labels are written around. Silybin is the principal single component of that family. We report both, separately, by HPLC, so a label claim can be traced to a number.
What assay grades do you supply?
The standard production grade is silymarin 80% by HPLC, with silybin available from 30% to 98% by HPLC. Alternative grades include silymarin 70% and a water-dispersible silymarin 20% grade for beverage and stick-pack applications. All grades are extracted with food-grade ethyl acetate or ethanol, and solvent residues are tested against ICH Q3C limits and declared on the COA.
What documents come with a milk thistle order?
Every shipment is accompanied by a batch-specific COA covering silymarin, silybin, loss on drying, total ash, residual solvents, heavy metals (lead, arsenic, cadmium) and microbiological results, plus the specification sheet and SDS. Allergen and non-GMO statements are provided on request, and a pre-shipment sample is drawn from the actual production lot.
Related: Milk Thistle Extract — full specification, grades and documentation.